Insulating structures such as buildings and homes is an important means of conserving resources both environmentally and economically. A common way to insulate buildings or homes is to install batts of fiberglass or blown fiberglass insulation around the exterior walls of the structure. To this end, fiberglass insulation materials are frequently and effectively used to insulate attics, crawl spaces, and vertical wall cavities. It is well established that such materials prevent heat from being transmitted across the insulated area regardless of whether the conditioned air was warmer or cooler than the external air. Specifically, in the construction and/or insulation of buildings, insulation is used between the interior wall and the external sheathing in the void defined by the framing material, the exterior sheathing, and the interior wall material (hereinafter called the “wall cavity”). The insulation can be placed between the framing members after installation of the exterior sheathing. For example, in residential construction an insulation batting may be installed between 2″×4″ wall framing, an oriented strand board exterior sheathing, and a drywall interior. Also prevalent in residential construction is the use spray-in or loose fill insulation in this same manner.
The benefits of tightly sealing a building so as to prevent air infiltration have been widely recognized as an important goal both environmentally and economically. For example, the EPA has emphasized the adverse effects of air leaking through a building envelope that is not well sealed. The leakage of air decreases the comfort of a residence by allowing moisture, cold drafts, and unwanted noise to enter and may lower indoor air quality by allowing in dust and airborne pollutants. Furthermore, air leakage may account for between 25 percent and 40 percent of the energy used for heating and cooling in a typical residence. The EPA has determined that the amount of air leakage in a house depends on two factors. The first is the number and size of air leakage paths through the building envelope. Primary sources of these leakage paths are joints between building materials, gaps around doors and windows, and penetrations for piping, wiring, and ducts. The second factor is the difference in air pressure between the inside and outside. Pressure differences are caused by wind, indoor and outdoor temperature differences (stack effect), chimney and flue exhaust fans, equipment with exhaust fans (dryers, central vacuums) and ventilation fans (bath, kitchen). The EPA has further stated that it is important to seal the building envelope during construction prior to installation of the drywall because once covered, many air leakage paths cannot be accessed and properly sealed. There are many products available for air sealing including caulks, foams, weatherstripping, gaskets, and door sweeps.
One technology that has been developed for the sealing of buildings is the use of spray-foam insulation. The application of spray-foam insulation to building structures has generally followed two divergent methodologies using a range of foam based materials. In one approach, a spray-foam insulation is applied to a building structure in a manner to completely fill the void (hereinafter referred to as “wall cavity”) between the outer sheathing and the inner wall substrate between the structural supports (hereinafter referred to as wall studs). In this application, the spray foam insulation replaces the use of other insulation materials such as fiberglass insulation batts, blown-in fiberglass insulation, or loose-fill cellulosic insulation. The second approach is to use spray-foam insulation in the corners of the wall cavities combined with a traditional batt or loose fill fiber insulation.
The limitations of both of these techniques are apparent by an examination of the spray-foam material. Traditionally, the spray-foam material was a rigid polyurethane foam. The rigid polyurethane foams were formed on-site by mixing polyols with isocyanates which are very reactive. The isocyanates used were typically aromatic isocyanates, such as diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI). To form a foam, the isocyanate component is combined with a polyol in the presence of a blowing agent and sprayed out of a nozzle onto the surface to be treated. One disadvantage is that the material is prone to crack or pull away from the surface being insulated either at the time of installation or upon aging. With cracks and gaps, the structure is susceptible to air infiltration.
There are several other limitations associated with the use of spray-foam insulation products. For example, they are typically derived from non-renewable chemical sources. The spray-foam process requires handling two highly reactive compounds that are mixed together in advanced proportioners using specialized foaming equipment. Not only is the installation equipment expensive, but it also requires advanced worker training and limits the environmental conditions under which the foam can be installed. The chemistry of making the foam requires a precise mix of the polyol and the isocyanate for the foam to have the prescribed properties; thus, operator or equipment error can easily result in the manufacture of sub-optimal foam. Finally, the installation of spray-foam results in the release of substantial volatile organic compounds and toxins. To protect workers from these chemicals, advanced personal protective equipment must be worn and the structure must be quarantined for a time sufficient for the vapors to dissipate. Dissipation of the vapors includes releasing the vapors into the environment where they are pollutants that contribute to the formation of smog.